Effects of Clay Content and Subfreezing Temperature on the Freeze-Thaw Deformation Properties of Clayey Soils

Abstract

Uneven ground deformation occurs in clayey soils during freeze-thaw (FT), which limits the sustainable operation of infrastructure in cold regions. It is, therefore, imperative to understand the soil deformation behavior and its mechanism. This study investigates the effects of clay content (5%, 10%, 15%, and 20%) and subfreezing temperature (-5oC, -10oC, and -15oC) on the soil FT deformation properties by isotropic isothermal FT tests. Meanwhile, the soil structure evolution was characterized via Nuclear Magnetic Resonance and X-ray Computed Tomography. The results indicated that the frost heave ratio (η) and thaw settlement coefficient (δ) non-linearly varied with clay content and subfreezing temperature. Specifically, the minimum η and δ were observed in specimens with 10% clay content, and the maximum η and δ were identified at -10oC. The effect of clay content on the η and δ can be attributed to the development of clay aggregate, while the impact of temperature on soil FT deformation is mainly due to the freezing of inter- and intra-aggregate pore water. The soil-water interaction was coupling influenced by clay content and subfreezing temperature. The pore size was significantly altered during FT. After FT, flake-like cracks were observed at the outer layer, whereas point-like ones formed in the center of the specimens. The contribution of pore size variation and crack development to the total volume change before and after FT was quantitatively analyzed. It demonstrated that pore structure change was more important for the total volume change in the specimens with lower clay content and a higher subfreezing temperature, whereas crack development contributed more to the total volume change in the rest of the specimens. This study can provide valuable guidance for constructing engineering projects in permafrost regions.

Keywords: Clayey soils, Clay content, Subfreezing temperature, Freeze-thaw deformation, Soil structure